The present invention relates to a technique effective if applied to a semiconductor integrated circuit device in which an on-chipped VCO (voltage-controlled oscillator) capable of performing switching of an oscillation frequency and a PLL circuit including the VCO in a loop are built, and to a technique effective for application to a communication semiconductor integrated circuit device suitable for use in a wireless communication system like, for example, a cellular phone, in which a transmission VCO for upconverting the frequency of a transmit signal and a PLL circuit are built.
A communication semiconductor integrated circuit device (hereinafter called “high frequency IC”), which combines a received signal or a transmit signal with a high-frequency local oscillation signal to downconvert or upconvert the frequency and which modulates the transmit signal and demodulates the received signal, has been used in a wireless communication system like a cellular phone.
As the cellular phone, a cellular phone of a dual band system has heretofore been known which is capable of handling signals lying in two frequency bands like GSM (Global System for Mobile Communication) lying in an 880 to 915 MHz band and DCS (Digital Cellular System) lying in a 1710 to 1785 MHz band, for example. There has recently been a demand for a cellular phone of a triple band system capable of treating with signals of PCS (Personal Communication System) lying in, for example, a 1850 to 1915 MHz band in addition to GSM and DCS. It is expected that the cellular phone needs to be adaptable to many systems. A voltage-controlled oscillator (VCO) used in the cellular phone adaptable to such plural systems needs to be wide in oscillation frequency range. When an attempt is now made to adapt one VCO to all frequencies, the sensitivity (hereinafter called “control sensitivity”) of an oscillation frequency with respect to a control voltage of the VCO increases, thus causing a problem that it becomes susceptible to externally-incoming noise and variations in power supply voltage.
Thus, the invention has been proposed which makes it possible to use a VCO while being switched to plural (16) frequency bands, thereby enabling a reduction in the control sensitivity of the VCO while a desired oscillation frequency range is being maintained (see patent document 1: Japanese Unexamined Patent Publication No. 2003-152535 (corresponding USP application: U.S filing date: May 14, 2004 (U.S. Ser. No. 10/495,611)). Incidentally, the present prior invention has adopted a system which previously measures actual frequencies in all frequency bands for the VCO prior to the start of its operation and stores the same in a memory and which compares information about the frequencies and the measured values of frequencies in the memory when oscillation frequency information is given, thereby to determine the optimum frequency band to be used.
On the other hand, efforts have recently been made to incorporate as many circuits as possible in one or several semiconductor integrated circuits in a cellular phone for the purpose of reducing the number of parts and achieving reductions in the size and cost of the device.
As one of them, there is known an attempt to incorporate or build a loop filter provided over a loop of PLL in a high frequency IC into a semiconductor chip.